In the present study, we analyzed the involvement of NLR on admission with the incidence of in-hospital mortality, AKI, and ETI in patients with COVID-19. The results showed that higher NLR on admission was significantly associated with all poor outcomes present in this study, even after adjustment for potential confounding factors.
Huang et al.  was the first research group to report COVID-19 and found that COVID-19 was related to ICU admission with high mortality. Chen et al.  reported a relatively high mortality for COVID-19 of up to 14.1%, which was higher than that reported in previous studies [7, 15, 16]. However, by July 23, 2020, over 15 million cases of COVID-19 had been reported by WHO, from almost every country in the world. The number of deaths was over 600,000 with mortality as high as 4.1%. In our study, the total number of deaths was 37, and the mortality was as high as 20.3%, which was higher than that of any research reported thus far. This was likely due to the large proportion of serious or critical patients admitted to Wuhan Union Hospital and the limitation of medical resources during the start of a disease outbreak.
Guan et al.  reported that, lymphocytopenia was present in over 80% of the patients on admission. In addition, Chen et al.  reported that compared with the recovered patients, non-survivors had a persistent and more severe lymphopenia. The WBC and neutrophil counts were also higher in non-survivors.  In our study, neutrophils and lymphocytes were associated with a prognosis in the primary outcome even after adjustment for age, BMI, and sex. However, these significant differences did not exist in the multivariable analysis. Although several guidelines suggest that lymphopenia may be associated with critical disease and even death. [3, 4]
Neutrophilia may be associated with cytokine storm caused by a viral invasion.  Lymphocytopenia is a significant feature of COVID-19 in critical patients. In 2005, Gu et al.  reported that it was the result of the destruction of lymphocytes caused by the destruction of cytoplasmic components after the targeted invasion of viral particles. Lymphocytopenia was also reported in critical patients infected with the MERS-CoV, which may be the result of the apoptosis of lymphocytes. [19, 20] A previous study suggested that the severity of lymphopenia reflects the severity of COVID-19. [6, 21] Organ dysfunction, including an acute renal injury, may be related to the direct effect of virus, hypoxia, and shock. The reason for this phenomenon could be that neutrophilia and lymphopenia were related to severe COVID-19 patients , but further study need to be performed.
In recent decades, several studies have reported on large differences in hematological components due to the systemic inflammatory response, which were subsequently used to predict the disease severity and outcomes. NLR, a simple, easily calculated and readily available parameter has been investigated for its use in some diseased states, including inflammatory conditions, cardiovascular disease, and carcinomas. [23–25] In recent years, several studies have reported that the use of NLR to evaluate associations between a viral [12, 13] involvement and prognosis of infected patients. There is reason to believe that it is reasonable to predict the prognosis of patients with novel coronavirus by NLR.
A recent study has implicated that NLR was an independent risk factor of the in-hospital mortality for COVID-19 patients. Of note, the value of all variables were the baseline data of laboratory examinations. It is possible that therapeutic manipulations may rapidly influence the value of NLR. For COVID-19 patients with a high mortality, it is very important to predict the prognosis using commonly obtained laboratory data on admission within 24 h.
Our study has certain limitations. First, this study design was that of a retrospective study, such that more detailed therapeutic responses will be needed. Several patients developed disorders of consciousness upon admission, which may have resulted in the involuntary omission of patients information (in particular, a detailed medical history). Missing data can lead to a bias in results. Second, the lack of effective antivirals  and corticosteroid  use may have also contributed to the poor clinical outcomes observed in certain patients. Moreover, the case fatality ratio reported in our study is not representative of the true mortality of COVID-19 patients, due to the large number of critically ill patients found in the Wuhan Union Hospital. Lastly, the interpretation of our findings may also be limited by the sample size.
Our research provides a preliminary insight into the identification of variables for the prediction of COVID-19 patient outcomes and serves as a basis for further detailed clinical and pathophysiological studies, which will also be necessary.